1. Field of the Invention
The present invention relates to a method of fusing commutator risers to an armature coils in an electric motor which is used, for example, in automotive electric parts.
2. Description of the Related Arts
In general, production of an electric motor of the kind described necessitates fusing an armature coils on an armature core to risers of a commutator. FIG. 5 illustrates a conventional method for accomplishing such fusing of commutator risers. According to this conventional method, a sub-electrode 6 is placed in contact with the outer peripheral surface of the commutator 4, and a plurality of main electrodes 7 which are radially arranged around the sub-electrode 6 are pressed onto the risers 5, thereby fusing the risers to the armature coil. This arrangement, however, requires anvil or support members 10 which are placed between the commutator and the armature coil, in order to receive the pressure exerted through the main electrodes 7. Consequently, the number of parts is increased so as to raise the cost. In addition, these support members 7 cannot satisfactorily receive the pressure. Furthermore, since the main electrodes 7 are arranged in a side-by-side fashion around the sub-electrode 6, it is necessary that the risers 5 have a large radial height, and the configuration of the armature core has to be determined in such a manner as to provide a space for accommodating the main electrodes 7, which undesirably limits the degree of freedom of design of the armature core.
In order to obviate this problem, a method as shown in FIGS. 6A to 6C in which through holes 3c are formed in the core part of the armature core 3, and sub-electrodes 6 (or riser support members) are inserted through these through holes 3c into contact with the back pressed onto the risers 5 which are backed by the sub-electrodes 6, thus accomplishing the fusing. This method, however, has a drawback in that, since no definite relationship is determined between the positions of the through holes 3c and the positions of the risers 5, some of the risers 5 may be hidden behind the ribs 3d which are positioned between the adjacent through holes 3c. It is therefore necessary to use an L-shaped specific sub-electrode 6 to back up such a riser 5. In addition, a troublesome work is required to circumferentially rotate such sub-electrode towards the riser 5 hidden behind the rib 3d. Thus, the method shown in FIGS. 6A to 6C is still unsatisfactory and needs improvement.